1. Field of the Invention
This invention relates to a conductive gasket for improving electrical grounding between adjacent conductive parts, and, more particularly, to a gasket for improving electrical grounding within a computing system between a slotted panel through which connectors of circuit cards extend for the attachment of external cables and brackets mounting such circuit cards.
2. Background Information
FIGS. 1 and 2 are fragmentary elevations of a conventional computing system 8 including a mother board 10 and a conventional circuit card 12 having a tab 14 inserted within a card edge connector 16 of the mother board 10. FIG. 1 is a fragmentary vertical cross-sectional elevation of the computing system 8, while FIG. 2 is a fragmentary rear elevation thereof.
The rear end 18 of the circuit card 12 includes a card bracket 20 attached to a slotted panel 22, forming part of the computing system, by means of a screw 24. An individual slot 26 within the slotted panel 22 provides a space through which an I/O connector 28 extends for attachment to an external cable (not shown). Thus the card 12 is rigidly held in place by the screw 24 near its top edge 30 and by the engagement of its tab 14 with the card edge connector 16 near its lower edge 32. The mother board 10 may be a relatively large system (or planar) board extending inwardly adjacent a cover 36 of the computing system. Alternately, the mother board 10 may be a riser board extending perpendicularly from the system (or planer) board to provide for the attachment of one or more circuit cards 12. Typically, the computing system 8 includes a number of card edge connectors 16 and a number of slots 26, each of which is located in a standard way relative to a connector 16 to provide for the installation of a standard type of circuit card 12. While each circuit card 12 has a card bracket 20, not all cards 12 have I/O connectors 28. Cards 12 without I/O connectors, which are not configured for attachment to external cables, include brackets 20 which are used to close an associated slot 26 within the slotted panel 22. When a circuit card 12 is not placed in one of the card edge connectors 16, the associated slot 26 is closed by a filler bracket 38, which is not attached to a circuit card 12. Like the card brackets 20, each filler bracket 38 is fastened in place using a screw 24.
Electrical contact between the card bracket 20 and the slotted panel 22 is typically used to provide for electrical grounding of circuits within the circuit card 12 and within an external cable (not shown) connected to the I/O connector 28. This contact may form a portion of multiple grounding points. Electrical contact between the card bracket 20 and the slotted panel 22 is also used to close a slot through which radio-frequency electromagnetic noise could otherwise be radiated to interfere with electronic communications.
A problem with this conventional approach arises from the uncertain nature of the electrical contact established between the card bracket 20 and the slotted panel 22. While specific contact pressure between the card bracket 20 and the slotted panel 22 is established adjacent the head of screw 24, the contact pressure at other locations between these parts depends on the slightly variable dimensions of parts, including their flatness.
A card bracket formed from a thin metal sheet, having a number of individual formed cantilevers to provide specific points for contact with a slotted panel, has been used in a number of circuit cards developed particularly for use with the IBM MICRO CHANNEL architecture. An example of this type of card bracket, configured particularly for use with a daughter card attached to the circuit card, is shown in U.S. Pat. No. 5,980,275. However, this type of card bracket must be used with a much different type of slotted panel having wide edges along which the contact cantilevers slide, and with cards not having formed brackets of the standard types used with the Industry Standard Architecture (ISA) and the Peripheral Card Interconnect (PCI) architecture. What is needed is a gasket providing specific contact locations which may be used with cards having such standard brackets, since such cards are widely available.
A number of conductive gaskets for various applications, other than the grounding of card brackets of slotted panels, are also formed to include a number of cantilevers providing specific points of contact. Such gaskets have a disadvantage of nesting together when they are shipped or otherwise handled in quantities, with the cantilevers of different gaskets interlocking so that the gaskets cannot easily be separated without damage. What is needed is a gasket configuration producing parts which can be handled and shipped together without this kind of nesting. Furthermore, such gaskets are often easily damaged during the handling and installation of associated parts, since the easily-twisted cantilevers may become snagged on other surfaces.
Conductive gaskets formed of fine-diameter woven conductive fibers or conductive fibers compressed into a matted, felt-like material have also been used for various applications other than the grounding of such card brackets. Gaskets formed in this way have disadvantages of a difficult fabrication process and of attendant relatively high costs.
U.S. Pat. No. 5,825,634 describes the use of an undulating or serpentine spring gasket in an assembly including a shielding cover fastened in place to extend along a portion of a surface of a circuit board. The spring extends between a peripheral edge of the cover and an electrical contact extending along the surface of the circuit board adjacent the peripheral edge. The relatively long and gentle undulations of the spring material produce alternating high and low areas. While a spring of this type can undergo relatively large deflections to provide a mechanically flexible interface between the mating parts, the resulting deflections of the spring, which cause each leg of the spring to lengthen as the spring is compressed between mating parts make it difficult to control the overall dimensions of the spring gasket in use. In the application of the present invention, i.e. in the grounding of card brackets to a slotted panel, overall dimensions must be carefully controlled, since a number of parts have to fit together in a small area.
Accordingly, it is a first objective of the present invention to provide a spring gasket causing electrical contact to be made at particular locations between a card bracket in a computing system and a slotted panel providing access to a circuit card I/O connector for external cables.
It is a second objective of the present invention to provide a spring gasket which is flexible, allowing electrical contact to occur despite variations in the dimensional configurations of adjacent parts.
It is a third objective of the present invention to provide a spring gasket in which the length of various legs within the gasket does not substantially change as the spring gasket is compressed.
It is a fourth objective of the present invention to provide a spring gasket which does not nest with other similar parts during storage or shipment.
It is a fifth objective of the present invention to provide a spring gasket which is not easily damaged by contact with adjacent parts during installation and handling.
According to a first aspect of the present invention, a conductive gasket for providing electrical conductivity between adjacent first and second conductive members separated in a first direction is provided. The conductive gasket includes a central web, a first plurality of contact bumps extending from the central web in the first direction; and a second plurality of contact bumps extending from the central web opposite the first direction, wherein contact bumps in the first and second pluralities of contact bumps are arranged in alternating patterns along the central web to include contact bumps in the first plurality of contact bumps adjacent contact bumps in the second plurality of contact bumps.